Monday, November 26, 2018

Researchers (1) from University of Birmingham present evidence supporting that proposition.

Remember the T lymphocytes,they arise from the bone marrow and trek to the thymus where they multiply and prosper then traveling to the lymph nodes and play a essential role in immune function.Decreased immune function and shrinkage of the thymus are well known effects of aging.

The authors studied immune function in 125 subjects aged 55-79 who had exercised regularly ( cycling) for many years.These were not elite athletes .They also studied age matched non exercisers and young adults.

The active group had higher T cell levels and higher levels of something called RTE which stands for recent thymic emigrants than did the less active control group and these levels were the same as the healthy young controls .

This finding lead some of the lay press to hype the findings in terms such as having the immune function of a 20 year old when you are 80 but only a selected aspect of immune function seemed well preserved and the authors found other aspects of the immune system (including numbers of B Cells) were the same in the active and the inactive group and not similar to the young controls.

So, 80 year old master cyclists may not have the immune function of a 20 year old but do have some aspects of immune function better preserved than the age matched sedentary controls and there is still another reason why active aging is different from sedentary aging .

1)Duggal NA, Major features of immunosenescence including thymic atrophy are ameliorated
by high levels of physical activity in Adulthood. Aging Cell 2018 Apr 17(2) Online published March 8 2018

Monday, November 19, 2018

In 1998, Haissaguerre et al (1) described atrial ectopy or premature atrial beats within the pulmonary veins as the trigger for atrial fibrillation.It seemed to be a particularly attractive theory for the origin of paroxysmal AF (PAF) and has also been proposed as a facilitator of continuation of AF to persistent AF.

This lead to the idea that electrical isolation of the pulmonary veins by burning atrial tissue would keep the ectopy from reaching the rest of the atrium .

And so Pulmonary vein isolation (PVI) really caught on being used for not only PAF but for persistent AF as well and ever since the electrophysiology world has awaited a randomized clinical trial answering the question does PVI decrease mortality in atrial fibrillation (AF). It is accepted dogma,backed by considerable experience that PVI is superior to medication treatment in suppressing AF and there is general agreement that restoration of sinus rhythm improves quality of life .A unanswered question was does PVI decrease risk of death associated with AF.

The Long-awaited CABANA trial was supposed to or at least hoped would provide an "Answer" to that question.

When the results of this large (2204 subjects) multi-center,multi national (https://www.acc.org/latest-in-cardiology/clinical-trials/2018/05/10/15/57/cabana) were announced there was no widespread celebration in the EP community. When the data were analyzed according to the standard statistical method used in randomized superiority clinical trials ( namely the "intention to treat" (ITT)) method), there was no difference in the primary outcome which was the combined end points of death,disabling stroke,serious bleeding or cardiac arrest between the ablation group and the treated with drugs group.Further using ITT analysis there was no significant difference between the two treatment arms for each of the components of the combined end point .

For ablation versus drug therapy :8% vrs. 9.2% with a hazard ratio of 0.86 (0.65-1.15, ) p=0.3 in regard to the primary endpoint.

There was no difference in death nor in serious stroke between the two arms of the study.

However looking at secondary outcomes- In regard to the category of death or cardiovascular hospitalization there was a significant difference.

There is more than one way to analyze data and results of the "per protocol " analysis gave consolation to the EP cardiologists.

The per protocol analysis showed: a significant decrease in the composite primary end point with ablation -ablation 7% versus drug10.9 % ( HR 0.57 , 0.50 -0.89) and decrease in all cause mortality in the ablation group , 7.5 % for drugs versus 4.4 % for ablation.

So intention to treat analysis indicated that ablation was not superior while per protocol analysis indicated that ablation was superior.Something for everyone.

Though heralded by some as a "game changer", I see nothing in the results changing any game. EP cardiologists are not likely to change their practice in any meaningful way Just look at the final sentence in the Conclusion slide presented at the American College of Cardiology meeting in August 2018:

"Ablation is an accepted treatment strategy for treating AF with low adverse event rates even in higher risk patients.". Since the study confirms what other data have shown namely that ablation converts AF to sinus rhythm more often than drugs and since sinus rhythm is associated with a better "quality of life" and the results are more durable why would EP docs change the way they are practicing ?

Wednesday, November 14, 2018

Aerobic exercise capacity is strongly linked to 02 max which is the product of the cardiac output ( stroke volume X heart rate) multiplied by the A-v 02 difference.

Five middle aged men who underwent aerobic training at age 20 in 1966 participated in a 6 month endurance training program in 1996.Their average 02 max increased 14% but there was no change in their maximal cardiac outputs. Their A-V 02 difference did increase by 10% accounting for the entire improvement in their aerobic power.

The increase in mitochondrial function brought about by aerobic exercise is well documented and the more mitochondrial the higher the 02 uptake by the exercising muscles.

1)McGuire, DK et al A 30 year followup of the Dallas Bedrest and training Study11Effect of age on cardiovascular adaptation to exercise training. Circulation2001 Sept 18 104 (12) 1358-66

Friday, November 09, 2018

The beneficial effect of prolonged endurance aerobic exercise on the aortic and great vessels may be as important or more important that its effects on diastolic function and favorable remodeling. First the aorta is not a stiff pipe. One model used to explain aortic function and the shape of the aortic pressure waves is the Windkessel effect model which considers the aortic and large elastic arteries as if it were an elastic buffering chamber which provides a cushioning or reservoir effect providing blood flow during diastole and damping the pulsatile flow. This reservoir effect flow is said to be as much as 40% of the stroke volume. The large elastic arteries act as capacitors , storing energy during systolic while bulging a bit and then pushing back or recoiling during diastole maintaining a more or less steady flow of blood and offering protection to the vulnerable arterial vessels of the brain and kidney to which excessive pulsatile flow may be harmful. The capacitance effect does not eliminate pulsatilty,of course ,the textbook normal diastolic blood pressure is 80 and not zero which is what it would be if the aorta were a lead pipe. With aging,and arguably more so with sedentary aging,the elastic vessels become less elastic, stiffer and provide less of the Windkessel effect reflected in higher systolic blood pressure, lower diastolic blood pressure (increased pulse pressure) and more rapid blood flow. This can measured by noninvasive measurement of pulse wave velocity with an higher velocity indicating stiffer arteries.Loss of the reservoir function. i.e.. a stiffer aorta and other great vessels increase the left ventricular afterload predisposing to left ventricular wall thickening. It is easy to find data supporting the claim that exercise will improve aortic compliance.As early as 1973 a report from the Baltimore Longitudinal Study on Aging (BLSA) (ref 1) indicated improved pulse wave velocity ,augmentation index and systolic blood pressure in older endurance athletes as compared with sedentary controls.Other more recent detailed physiologic studies have confirmed that finding. Gates et al(2) studied men with varying exercise histories in three different age groups and reported that the regular endurance trained subjects has lower large artery stiffness as measured by a reduced aortic pulse wave velocity.An excellent, detailed exposition of the physiology of the adaptation of the aorta to endurance exercise can be found in full free text in reference 3.

Thursday, November 08, 2018

Dr. J Kin along with Dr. Aaron Baggish, who directs the Cardiovascular Performance Program at MGH, studied a group of NCAA Div.1 college football lineman and compared results with non-lineman over the course of a single season. (1)

They reported that the lineman were all normotensive preseason while post season , 30% had developed Stage one hypertension and 60% developed pre-hypertension. The non-lineman improved their Global Longitudinal Strain measurement (as determined by speckle echocardiography)while the lineman worsened theirs.Concentric hypertrophy was noted in the lineman while the non-linemen displaced eccentric hypertrophy.

This was after a single season.Consider that many high school player play for four years and a number then have a college career.

The authors concluded:

... participation at a lineman field position may lead to a form of sport-related myocardial remodeling that is pathologic rather than adaptive. Future study will be required to determine if targeted efforts to control blood pressure, minimize weight gain, and to include an element of aerobic conditioning in this subset of athletes may attenuate this process and translate into tangible downstream health benefits."

I have blogged before about the occurrence of CTE in collegiate football players quoting a study from the Boston University CTE center. The authors reported 48 cases who only played high school and college ball.

There have also been several articles reporting imaging abnormalities in young players with both concussive and subconcussive head trauma.Now we seem to have evidence of subclinical heart damage that like subconcussive blows might lead to downstream health problems.